20 Executor Framework Interview Questions and Answers

The Executor framework is a set of Java classes that provide a simple and efficient way to manage threads. When applying for a position that involves Java development, it is likely that you will be asked questions about the Executor framework. Reviewing common questions and knowing how to answer them can help you prepare for your interview and increase your chances of getting the job.

Executor Framework Interview Questions and Answers

Here are 20 commonly asked Executor Framework interview questions and answers to prepare you for your interview:

1. What is the Executor Framework?

The Executor Framework is a set of Java classes that provide a standard way of executing tasks concurrently. The framework provides a number of features that make it easy to write concurrent code, including a thread pool that can be used to manage a large number of tasks.

2. Can you explain what an executor service is and how it works?

An executor service is a thread pool that can be used to schedule and execute tasks. It works by creating a pool of threads that can be used to execute tasks. When a task is submitted to the executor service, it will be added to a queue. A thread from the pool will then be chosen to execute the task.

3. Why use the Executor framework instead of Threads to execute tasks in Java?

The Executor framework provides a number of benefits over using Threads directly. First, it separates the task of creating and managing threads from the actual execution of tasks. This can lead to more efficient code, as well as code that is easier to debug and maintain. Additionally, the Executor framework provides a number of features that can make it easier to manage tasks, such as the ability to schedule tasks, and to provide thread pools that can be used to reuse threads.

4. Can you give me some examples of where you would use the Executor Framework?

The Executor Framework is a Java API that can be used to manage concurrency in your applications. It provides a way to run tasks in the background, and to schedule tasks to be run at a later time. You might use the Executor Framework to run tasks that perform database operations, or to run tasks that process data from a web service.

5. How can you create your own thread pool in Java using the Executor framework?

You can create your own thread pool in Java using the Executor framework by creating a ThreadPoolExecutor and passing in a number of threads that you want to use, as well as a ThreadFactory to create new threads.

6. When should you choose a fixed-size thread pool over a cached thread pool?

A fixed-size thread pool is best when you know exactly how many tasks will be coming in and you want to ensure that each task is executed in a timely manner. A cached thread pool is better when you are not sure how many tasks will be coming in or how long each task will take to execute.

7. Which classes are used for creating threads on demand with the Executor Framework?

The ExecutorService and Executors classes are used for creating threads on demand with the Executor Framework.

8. What do you understand about callable and future objects in the context of the Executor Framework?

Callable and Future objects are two different ways of representing a task that is to be executed by an Executor. A Callable is simply a representation of a task that can be executed, while a Future object wraps a Callable and provides additional methods for managing its execution. Future objects are generally used when you want to be able to track the progress of a task or cancel its execution.

9. What’s the difference between Runnable and Callable interfaces?

Runnable is a functional interface that can be used to encapsulate a task that can be executed by an Executor. A Runnable cannot return a result or throw a checked exception.

Callable is also a functional interface that can be used to encapsulate a task that can be executed by an Executor. Unlike Runnable, a Callable can return a result or throw a checked exception.

10. Can you explain the life cycle of a task that’s submitted to an Executor Service?

When a task is submitted to an Executor Service, it first enters a queue. The Executor Service then assigns a thread to the task, and the task begins running. If the task is interrupted or fails, it is removed from the queue and the Executor Service moves on to the next task.

11. Can you tell me which API calls are available to control the execution of tasks within the Executor framework?

The Executor framework provides a number of different ways to control the execution of tasks. The most basic way to do this is to simply submit tasks to the Executor and let it manage their execution. However, you can also use the submit() method to submit tasks and receive a Future object that can be used to track the task’s progress and check for results. Additionally, the ExecutorService interface provides methods such as shutdown() and awaitTermination() that can be used to shut down an Executor and wait for all tasks to complete.

12. When does an executor service shutdown?

An executor service shuts down when it is no longer needed or when the program shuts down.

13. What happens if you submit a new task after calling shutdown() on an ExecutorService?

If you submit a new task after calling shutdown() on an ExecutorService, then the task will be rejected and an exception will be thrown.

14. What does the awaitTermination method do?

The awaitTermination method is used to block the current thread until all tasks in the executor have completed execution, or the timeout period has elapsed.

15. What’s the best way to handle exceptions thrown by tasks executed using the Executor framework?

The best way to handle exceptions thrown by tasks executed using the Executor framework is to use a try-catch block within the run() method of the task. This will ensure that any exceptions that occur during the execution of the task are properly handled and that the task can continue to run.

16. How do you cancel a running task from inside the executor framework?

You can cancel a running task from inside the executor framework by using the Future object associated with the task. The Future object provides a method called cancel() which can be used to cancel the task.

17. What are some common problems that arise while working with an Executor framework?

Some common problems that can arise while working with an Executor framework include:

-Threads getting stuck in an infinite loop
-Threads blocking each other
-Threads starving each other
-Deadlocks

18. What are the different ways of submitting a task to the executor framework?

There are four different ways of submitting a task to the executor framework:

1. Executor.execute() – This method simply submits the task to the executor for execution.
2. ExecutorService.submit() – This method submits the task to the executor and returns a Future object.
3. ExecutorService.invokeAll() – This method submits a collection of tasks to the executor and returns a list of Future objects.
4. ExecutorService.invokeAny() – This method submits a collection of tasks to the executor and returns the result of one of the tasks.

19. Is it possible to wait until all tasks have completed before shutting down an executor service? If yes, then how?

Yes, it is possible to wait until all tasks have completed before shutting down an executor service. This can be accomplished by using the awaitTermination() method. This method will block until all tasks have completed or the specified timeout has elapsed, whichever comes first.

20. What are some important features of the Executor Completion Service class?

The Executor Completion Service class is designed to help manage the execution of a large number of tasks. It provides a way to track the status of tasks as they are executed, and also allows tasks to be submitted in advance of their execution. This can be helpful in situations where tasks need to be executed in a specific order, or where tasks may take a long time to complete.